Gas heaters that heat a radiating body with combustion heat produced by the burning of fuel gas and that heat industrial materials and food and the like with radiating heat from the radiation surface of a radiating body are widely gaining popularity.
In relation to this kind of combustion heater, art has been disclosed that makes a sealed structure from a lead-in passage that guides fuel gas to a combustion chamber and a lead-out passage that guides the exhaust gas burned in the combustion chamber to outside the body, makes the lead-in passage and the lead-out passage adjacent, and increases the thermal efficiency by preheating the fuel gas prior to combustion by the heat of the exhaust gas (for example, refer to Patent Document 1).